A good writer is entertaining and keeps me up all night reading. They create an illusion where you are looking through the pages and just see the story and you forget about plot devices, how it's written, and cliches/tropes and you just want to know what happens. (e.g. I normally pay attention to the writing in a book when I'm reading it, but Hunger Games sucked me in so much that I didn't even realise that it was written in present tense until halfway through the second book.)

I think a good writer is someone who can effectively spin a good tale in their own way. While those authors who cater to the masses can be considered good by certain people (Ex. A lot of romance or mystery writers create hundreds of novels, all with the same plot, and make millions from it), I like the ones who break from the norm and follow their own path. While some of the stranger titles can be a little crazy, sometimes silly-seeming, or sometimes uneffective in general, it's the real geniuses who break away from the norm. It also takes literary genius to create something new (mystery novels haven't been around forever, you know), and those people are definitely seen as "good" because they forged entirely new parts of the art.

When it comes to the growing artist, I think there are a few factors that can decide things:
1) Effective use of tools. While spelling and grammar isn't everything, the new writer needs to be as polished as possible so their work gets read. Even poor formatting choices has turned me away from perfectly good pieces. If you want to be seen, you have to use the language correctly.

2) Dedication. Some people just write for fun, so they could go months or years without writing, and that's okay to them. Truly, while those authors could be good in their own right (Emily Dickenson wrote this way, as a hobby), if they want to please those who think commercial success makes an author good, they'll need more than the occassional good piece. To me, a good writer is someone who works on their craft and improves over the years. Writers might be good, but if they stick with the same old show all the time, it gets a little dry.

3) Success. A lot of people think that being a good writer is to be published and become richer than the Queen (like JK Rowling). While I would love to be that kind of successful, what makes a writer good could be the small successes. For instance, if you make someone's day with your uplifting piece, you're successful. If you work for days on a research piece and it receives a high mark or rave reviews, you're successful. If you finally finished that piece that's been bugging you for years, you're successful. Personal success is just as important as commercial success, if not more so. You're not going to get commercial success until you can meet small goals.

Finally, I think it's a personal thing too. I think we're all familiar with the Harry Potter V Twilight debate, and everyone has a side on the matter (whether it's for one, both, or neither). That's probably the best example to show how personal preferences determine what you'll think. I'm sure there are some people out there who think Shakespeare was horrible (not just because they can't read Old English or because they're forced to read it). I, personally, don't like some of those big names that push out books without changing much about them.

Another thing about growing writers: Don't give up on yourself. Some of my old pieces were horrible, and I knew it then, but I didn't let it get me down. I kept up my writing, and I've improved so much. I'm not going to call myself the best, but I think I have a lot of potential. I like writing, too, and I'd love to make a career of it. But I'm not going to let a bad piece from the past determine if that's a reachable goal or not. Basically, have fun with it. It's all yours anyway.

I'm not going to say i'm a good writer because I have just started writing only a few months ago. However one thing I think is important of a good writer is if they can make the reader feel like they are in the story. For example, if it was say for a example a horror story, I would want to feel as scared as the characters are. Or looking from a first person point of view, I would want to see the which characters are scared, which ones are brave, the ones that will most likely do something stupid when things heat up.

To me it's all about emotions and being in the story, this would be important to me. But of course to create a environment which causes emotions, you need to describe the environment in a way to make people want to pay attention to it.

I don't know what makes writers good, but I know what makes me a good writer.

Characters.

Plots are important, and grammar also, but as far as I know, people remember the characters the most. The first thing that people talk about when seeing The Dark Knight, for example, isn't the intense plot, but rather how awesome the Joker was or how goofy Batman's voice was. When people talk about LotR, it's usually to say either that so-and-so is awesome or that Sam and Frodo were totally gay (totally ship that!). Harry Potter? How awesome so and so character was while so and so character was a pain in the ass.

I know how to write characters.

Most people don't really know what makes a plot good, even other writers. They may say they know what it is, but you don't, because your characters decide the plot for you. The quality of the plot is connected to the quality of your characters. If the story has a villain, the plot can be as intense as the smartest bad guy (I think Bruce Willis said that, but don't hold me to it). You can come up with a multi-layered, complex plot, but that's irrelevant if your characters stink. If you need an example EVERYONE knows about, Star Wars prequels. Plots were complex, even fairly intense. No one gave a crap because the characters were at best dull and at worst painful to watch.

Now, what makes a good character? Humanity. If the readers can relate and sympathize with the characters, that's good. Actually, sympathy is good, but empathy is what we need to aim for. They have to make sense. They have to have a hint of vulnerability. They can't be driven by a single emotion the whole while. Also, they grow and develop--or even regress--as circumstances change, like all humans do. They have to exist on their own playing field, and not do things just because the plot says so.

If you have good characters, that's what readers come back to. That's what they latch onto. That's who they write fanfiction about. If you want to be a good writer, learn to write good characters.